By PPN News Staff

The FDA granted a new indication for burosumab-twza (Crysvita, Ultragenyx Pharmaceutical) injection to treat patients aged 24 months and older with tumor-induced osteomalacia (TIO), a rare disease that is characterized by the development of tumors that cause weakened and softened bones. 

The tumors associated with TIO release a peptide hormone?like substance known as fibroblast growth factor 23 (FGF23) that lowers phosphate levels.

“Treatment for TIO focuses on identifying and removing the tumor that causes the disease. However, when that is not possible, Crysvita can help increase the levels of phosphate in the blood,” said Theresa E. Kehoe, MD, the acting director of the Division of General Endocrinology in the FDA’s Center for Drug Evaluation and Research. 

FGF23 regulates levels of phosphate, an electrolyte that plays important roles in bone maintenance, energy production by cells and nerve function. When there is insufficient phosphate in the body, bones begin to soften and weaken, causing osteomalacia.

The safety and efficacy of burosumab-twza were evaluated in two studies that together enrolled 27 adults with TIO. In both studies, patients received burosumab-twza every four weeks. In the first study, half of patients achieved normal phosphate levels through week 24 and maintained normal or near normal levels through week 144. In the second study, 69% of participants achieved normal phosphate levels through week 24 and maintained normal or near normal levels through week 88. The results of bone scans for patients in the first study also indicated healing of the bone lesions related to osteomalacia.

Hypersensitivity reactions, such as rash and hives, were reported. Patients should be told that if serious hypersensitivity reactions occur, they should stop taking burosumab-twza and talk to their health care provider about further medical treatment. 

Additionally, higher than normal levels of phosphorus may be associated with an increased risk for nephrocalcinosis.

The most common side effects reported in adults with TIO taking burosumab-twza were tooth abscess, muscle spasms, dizziness, constipation, injection site reaction, rash and headaches.

Patients taking oral phosphate or active vitamin D, those who have serum phosphate levels within or above the normal range for their age, and patients with severe kidney impairment or end-stage renal disease should not take burosumab-twza.

Crysvita is also approved to treat adults and children aged 6 months and older with X-linked hypophosphatemia, which causes low levels of phosphate in the blood and leads to impaired bone growth and development in children and adolescents. 

—From FDA press materials